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SN74AUP3G17: Using these schmitt triggers at cryogenic temperatures; do they contain any BJTs?

6058543
Prodigy 30 points
Part Number: SN74AUP3G17

Hi,

My question is as in the subject line. When trying to use these devices at cryogenic temperatures (less than 10mK), they appear to freeze out and not work at all. This suggests to me that this part contains BJTs somewhere in the circuit, as other tests have shown that purely digital CMOS circuits are not affected in this way by extremely low temperature.

Can someone confirm if the part contains BJTs or if I'm missing something? Are there any known low power schmitt triggers that are guaranteed to have no BJTs in them at all?

Many thanks

  • 0
    TI__Mastermind 44655 points

    Hi Welcome to the Forums!

    No these parts do not contain BJTs, but they do have a recommended operating temp which is being violated at that cold temp so I don't expect them to work. Please refer to the datasheet for the spec TA spec.

  • 0 in reply to Dylan Hubbard
    Prodigy 30 points

    Thanks for the confirmation Dylan,

    Despite the operating temp being grossly violated, I would still hope they would work as they are essentially digital devices, and other tests we've done have shown that MOSFETs on their own work at these temps, as well as FPGAs.

    I will continue to investigate different ideas to see what we can do. I don't suppose you have a recommendation for schmitt triggers that can be used at cryo temperatures? ;)

    Thanks again

    Matt

  • 0
    Guru 278840 points

    The ESD protection circuits might contain BJTs; the following is documented for AHC family devices (I don't know how much AUP is different):

    And CMOS devices contain parasitic BJTs:

    I suspect you have to try to build a Schmitt trigger from discrete MOSFETs.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 44655 points

    Hi Matt,

    If you dig down deep into CMOS physics then you will find parasitic BJTs (as Clemens has posted), but this is something you would also encounter with an FPGA so I don't see how this would be the issue. I wish I could provide more assistance since this sounds like a very 'cool' ;) project, but even our logic devices rated for Space applications don't have an operating temp that low. 

  • 0 in reply to Clemens Ladisch
    Prodigy 30 points

    Thanks Clemens and Dylan for your help with this

    Indeed the parasitics and esd devices are there, but if they freeze out in the cold they should just appear like resistors on the order of many GΩ I believe? Shouldn't make everything die completely.

    Looking into it though, I think depending on the exact architecture of these schmitt triggers, probably what is happening is something in a bias circuit somewhere is being exaggerated way out of the nominal operating region, as I believe the differences between PMOS and NMOS gm gets significantly exaggerated in the cold temperatures, so that could be the problem.

    @Clemens, I think your suggestion for building a trigger from discrete transistors is on the table for me now! Then I will be able to fully poke around in the design and see what happens when it's cold!

    Thanks again both for your help

    Matt